Glass fiber is an inorganic fiber material that can be used to reinforce resins to produce composite materials with good performance. As a reinforcing base material for advanced composite materials, high-modulus glass fibers were originally used mainly in the national defense industry, such as aeronautic, aerospace and military industry. With the progress of science and technology and the development of economy, high-modulus glass fibers have been widely used in civil and industrial fields such as wind blades, pressure vessels, offshore oil pipes, and auto industry.
The original high-modulus glass compositions were based on an MgO—Al2O3—SiO2 system, and a typical composition was the S-2 glass developed by OC company of US. Its modulus is 89-90 GPa; however, the production of S-2 glass is excessively difficult, as its forming temperature is up to about 1571° C. and its liquidus temperature is up to 1470° C. and therefore, it is difficult to realize large-scale industrial production. Then OC company gave up the production of S-2 glass fiber and assigned the patent to AGY company of US.
Thereafter, OC company has developed HiPer-tex glass. Its modulus is 87-89 GPa, which was a trade-off for production scale by sacrificing some of the glass properties. However, since these designed solutions just made a simple improvement on the S-2 glass, the forming temperature and liquidus temperature of the glass fiber were still high and the production of glass remained highly difficult, it is also difficult to realize large-scale tank furnace production. Then OC company gave up the production of HiPer-tex glass fiber and assigned the patent of HiPer-tex glass fiber to 3B company of Europe.
Saint-Gobain of France has developed R glass that is based on an MgO—CaO—Al2O3—SiO2 system, and its modulus is 86-89 GPa. However, the total content of SiO2 and Al2O3 remains high in the traditional R glass, and there is no effective solution to improve the crystallization performance, as the ratio of Ca to Mg is inappropriately designed, thus causing difficulty in fiber formation as well as a great risk of crystallization, high surface tension and fining difficulty of molten glass. The forming temperature is up to about 1410° C. and the liquidus temperature is up to 1350° C. All these have caused difficulty in attenuating glass fiber and consequently resulting in realizing large-scale tank furnace production.
Nanjing Fiberglass Research & Design Institute Co. Ltd in China has developed an HS2 glass having a modulus of 84-87 GPa. The HS2 glass mainly comprises SiO2, Al2O3 and MgO, and certain amounts of Li2O, B2O3, CeO2 and Fe2O3 are also introduced; its forming temperature is only about 1245° C. and its liquidus temperature is 1320° C. Both temperatures are much lower than those of S glass fiber. However, since its forming temperature is lower than its liquidus temperature thus resulting in a negative ΔT value, which is unfavorable for the control of glass fiber attenuation, the forming temperature has to be increased and specially-shaped tips of bushing have to be used to prevent a glass crystallization phenomenon from occurring in the fiber drawing process. This causes difficulty in temperature control and also makes it difficult to realize large-scale tank furnace production.
In summary, we have found that, various kinds of high-modulus glass fibers at this stage generally face production difficulty in large-scale tank furnace production, such as high liquidus temperature, high crystallization rate, high forming temperature, high surface tension and fining difficulty of molten glass, and a narrow temperature range (ΔT) for fiber formation and even a negative ΔT. For this reasons, most companies tend to reduce the production difficulty by sacrificing some of the glass properties. Thus, the modulus of the above-mentioned glass fibers cannot be improved with the growth of production scale, and the modulus bottleneck has long remained unresolved in the production of the S glass fiber.